Method of operating a vehicle under frozen diesel emission fluid conditions

ABSTRACT

A method of controlling a vehicle includes determining if a diesel emission fluid is at least partially frozen, and determining if the vehicle is currently operating in a low diesel emission fluid inducement protocol. If the vehicle is not currently operating in the low diesel emission fluid inducement protocol, and the diesel emission fluid is at least partially frozen, then a temporary minimum diesel emission fluid mass may be defined to prevent entry of the vehicle into the low diesel emission fluid inducement protocol.

TECHNICAL FIELD

The invention generally relates to a method of controlling a vehiclethat uses a diesel emission fluid stored in a tank.

BACKGROUND

Diesel emission fluid is used in conjunction with a selective catalyticreduction catalyst to reduce oxides of nitrogen in the exhaust of thevehicle. The diesel emission fluid is stored in a tank disposed on thevehicle. The tank may include three discrete level sensors to determinethe level of diesel emission fluid in the tank, i.e., the mass of thediesel emission fluid remaining in the tank. Additionally, the discretelevel sensors may be utilized for refill detection when new dieselemission fluid is added to the tank. When the diesel emission fluid isthawed, i.e., in a liquid state, the vehicle operates in a non-frozendiesel emission fluid protocol. When in the non-frozen diesel emissionfluid protocol, the mass of the diesel emission fluid is calculated byan algorithm, i.e., software, that evaluates the level of the dieselemission fluid in the tank based upon filtered signals from the threediscrete level sensors. However, the diesel emission fluid must slosharound in the tank in order for the mass determination of the dieselemission fluid to function properly. Accordingly, if the diesel emissionfluid is frozen and does not slosh around in the tank, the massdetermination of the diesel emission fluid is not accurate, and does notaccurately reflect the level and/or mass of the diesel emission fluid inthe tank. Additionally, when the diesel emission fluid is in the frozenstate, the discrete level sensors may not function and will notrecognize that the diesel emission fluid is at or above the discretelevel sensors.

The diesel emission fluid freezes at approximately negative elevendegrees Celsius (−11° C.). The tank includes a heater that keeps thediesel emission fluid thawed, or to thaw the diesel emission fluid whenfrozen. However, under certain ambient conditions, the diesel emissionfluid may still freeze.

If the level and/or mass of the diesel emission fluid in the tank fallsbelow a pre-determined level when considering the average consumptionrate of the diesel emission fluid by the vehicle, the vehicle may berestricted to operation in a low diesel emission fluid inducementprotocol. When operating the low diesel emission fluid inducementprotocol, the speed of the vehicle is restricted to induce an operatorof the vehicle to refill the tank. Once the software determines that thetank has been refilled with the diesel emission fluid, the vehiclediscontinues the low diesel emission fluid inducement protocol, and ispermitted to operate as normal. However, if the diesel emission fluidfreezes before the refill of the tank is detected, the vehicle maycontinue to be restricted to the low diesel emission fluid inducementprotocol.

SUMMARY

A method of controlling a vehicle that utilizes a diesel emission fluidstored in a tank is provided. The method includes determining if thediesel emission fluid is at least partially frozen, determining if thevehicle is currently operating in a low diesel emission fluid inducementprotocol, and defining a temporary minimum diesel emission fluid masswhich may be used to prevent initiation of the low diesel emission fluidinducement protocol. The temporary minimum diesel emission fluid mass isdefined when the vehicle is not currently operating in the low dieselemission fluid inducement protocol, and when the diesel emission fluidis at least partially frozen.

Accordingly, defining the temporary minimum diesel emission fluid massmay be used to prevent the vehicle from entering into the low dieselemission fluid inducement protocol when the diesel emission fluid isfrozen, and the vehicle would otherwise fail to properly sense theactual level of diesel emission fluid in the tank.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing a method of controlling a vehicle thatutilizes a diesel emission fluid stored in a tank.

DETAILED DESCRIPTION

Referring to FIG. 1, a method of controlling a vehicle is generallyshown at 20. The vehicle utilizes a Diesel Emission Fluid (DEF), whichis stored in a tank that is disposed on the vehicle. The DEF is used inconjunction with a selective catalytic reduction catalyst to reduceoxides of nitrogen in the exhaust of the vehicle. The tank may includethree discrete level sensors, which are used to determine the level ofthe DEF in the tank, i.e., the mass of the DEF remaining in the tank.Additionally, the discrete level sensors may be utilized for refilldetection when new DEF is added to the tank.

The mass of the DEF is used to calculate the distance that the vehiclemay be driven before running out of the DEF. This calculation is basedon a rolling average of the consumption rate of the DEF and the mass ofthe DEF remaining in the tank.

When the DEF is thawed, i.e., in a liquid state, the vehicle operates ina non-frozen DEF protocol. When in the non-frozen DEF protocol, the massof the DEF is calculated by an algorithm that evaluates the level of theDEF in the tank based upon filtered signals from the three discretelevel sensors. However, the DEF must slosh around in the tank in orderfor the discrete level sensor filtering method to function properly.Additionally, when the DEF is in the frozen state, the discrete levelsensors may not function and will not recognize that the DEF level is ator above the discrete level sensors. Accordingly, if the DEF is frozenand does not slosh around in the tank, the mass determination of the DEFis not accurate, and does not accurately reflect the level and/or massof the DEF in the tank. For example, if the DEF is completely frozen,the mass determination of the DEF based upon the filtered signals fromthe three discrete level sensors may indicate that the tank is empty,i.e., no DEF, and cause the vehicle to operate in a low DEF inducementprotocol, whereby the speed of the vehicle is restricted to induce anoperator of the vehicle to add DEF. Therefore, when the DEF is frozen,or at least partially frozen, the vehicle operates in a frozen DEFprotocol. When in the frozen DEF protocol, the vehicle bypasses the massdetermination based upon the filtered signals from the three discretelevel sensors, and instead initializes the DEF mass with the last knownvalue of the DEF mass remaining in the tank. The strategy thencalculates the DEF mass remaining by subtracting from the initializedvalue the mass of the DEF that has been dosed. Additionally, when in thefrozen DEF protocol, the DEF tank mass calculated as previouslydescribed is not allowed to drop below a calibratable minimum massthreshold which may be used to prevent the vehicle form entering the lowDEF inducement protocol, thereby allowing normal operation of thevehicle when the DEF is frozen.

The vehicle may include a controller, such as a computer and/or anengine control unit that is configured for controlling the operation ofthe vehicle. The controller may include, but is not limited to, allsoftware, hardware, memory, sensors and algorithms required to sense,store, and manipulate all aspects of the vehicle associated with theprovided method 20. As such, it should be appreciated that the method 20may be embodied as a program operable on the controller.

The method 20 includes defining a frozen DEF temperature, block 22. Thefrozen DEF temperature may be defined as the temperature at which theDEF freezes. For example, the frozen DEF temperature may be defined toequal negative eleven degrees Celsius (−11° C.). Alternatively, thefrozen DEF temperature may be set slightly higher than the temperatureat which the DEF freezes to provide a margin of safety. It should beappreciated that the frozen DEF temperature is dependent upon thechemical composition of the DEF used, and may vary from the negativeeleven degrees Celsius (−11° C.) described above.

The method 20 further includes determining if the DEF is at leastpartially frozen. Determining if the DEF is at least partially frozenmay include sensing a temperature of the DEF in the tank, block 24. Thetemperature of the DEF may be sensed in any suitable manner, includingbut not limited to, sensing the temperature of the DEF in the tank witha sensor disposed in.

Determining if the DEF is at least partially frozen further includesdetermining if the engine of the vehicle is operating or is notoperating, block 26. The engine control unit may be queried to determineit the engine is operating, i.e., running, or if the engine is notoperating, i.e., turned off. If it is determined that the engine is notoperating, indicated at 28, then determining if the DEF is at leastpartially frozen further includes defining a minimum engine off time,block 30, and measuring an engine off time period, block 32. The minimumengine off time ensures that enough time has elapsed since the enginehas been turned off, i.e., is not operating, that any heat from theengine and/or from a tank heater configured for heating the DEF tankdoes not affect the temperature reading of the DEF. The minimum engineoff time is the amount of time that is required for trapped heat todissipate from around the tank, and may vary with the size of tank andthe location of the tank within the vehicle. The minimum engine off timemay be set to any time period, such as but not limited to, a twenty (20)minute time period. The engine off time may be measured in any suitablemanner, including but not limited to measuring the engine off time withan internal clock of the vehicle or querying the engine control unit.

If the engine is not operating, then determining if the DEF is at leastpartially frozen further includes determining if the sensed temperatureof the DEF in the tank is less than the frozen DEF temperature orgreater than the frozen DEF temperature, and if the measured engine offtime period is less than the minimum engine off time or greater than theminimum engine off time, block 34. When the engine is not operating, theDEF is determined to be at least partially frozen when the sensedtemperature of the DEF in the tank is less than the frozen DEFtemperature, and the measured engine off time period is greater than theminimum engine off time, indicated at 36. Alternatively, the DEF isdetermined to not be frozen when the sensed temperature of the DEF inthe tank is greater than the frozen DEF temperature, and the measuredengine off time period is greater than the minimum engine off time,indicated at 38.

When it is determined that the vehicle is operating, indicated at 40,then determining if the DEF is at least partially frozen furtherincludes defining a minimum ambient air temperature limit, block 42, andsensing an ambient air temperature, block 44. Because the engine isoperating and producing heat, and the tank heater may be operating toheat the DEF, the measured temperature of the DEF alone may notaccurately reflect whether the DEF is at least partially frozen. Theminimum ambient air temperature limit is a temperature that issufficiently greater than the frozen DEF temperature, to ensure that theDEF is not frozen. The minimum ambient air temperature may be set to anytemperature, depending upon the chemical composition of the DEF. Forexample, the minimum ambient air temperature may be defined as, but isnot limited to, negative five degrees Celsius (−5° C.). The ambient airtemperature may be sensed in any suitable manner, including but notlimited to a temperature sensor disposed on the vehicle.

When the vehicle is operating, determining if the DEF is at leastpartially frozen further includes determining if the sensed temperatureof the DEF in the tank is less than the frozen DEF temperature orgreater than the frozen DEF temperature, and if the sensed ambient airtemperature is less than the minimum ambient air temperature limit orgreater than the ambient air temperature limit, block 46. When theengine is operating, it is determined that the DEF is not frozen whenthe sensed temperature of the DEF in the tank is greater than the frozenDEF temperature and has remained so for at least a minimum thaw time,and the sensed ambient air temperature is greater than the minimumambient air temperature limit and has remained so for at least theminimum thaw time, indicated at 48. In order to ensure that the DEF iscompletely thawed, the conditions that the sensed temperature of the DEFin the tank is greater than the frozen DEF temperature and the sensedambient air temperature is greater than the minimum ambient airtemperature limit are required to be maintained for the minimum thawtime. The minimum thaw time may be defined as any suitable time period,including but not limited to, four hours. It is determined that the DEFis at least partially frozen when the sensed temperature of the DEF inthe tank is less than the frozen DEF temperature, and the sensed ambientair temperature is less than the minimum ambient air temperature limit,indicated at 50. Alternatively, instead of monitoring the temperature ofthe DEF in the tank, actively heating the DEF in the tank with the tankheaters may be used to determine if the tank is at least partiallyfrozen. In this situation, the DEF in the tank is considered to not beat least partially frozen if the vehicle is operating, the DEF tankheater is not heating, and the ambient air temperature is greater than aminimum threshold for a minimum thaw time.

When it is determined that the DEF is not frozen, indicated at 38 and48, then the method 20 further includes operating the vehicle in thenon-frozen DEF protocol, block 52. As described above, the non-frozenDEF protocol allows for the level of the DEF to be calculated based uponthe filtered signals from the three discrete level sensors in the tank.Accordingly, if the vehicle was previously operating in the frozen DEFprotocol and it is determined that the DEF is no longer frozen, i.e.,not frozen, then the vehicle switches from the frozen DEF protocol backto the non-frozen DEF protocol.

The method 20 further includes determining if the vehicle is currentlyoperating in a low DEF inducement protocol, block 54. If, when thevehicle is operating in the non-frozen DEF protocol and the distanceremaining of the DEF is calculated to be less than a minimum level, thenthe vehicle may begin operation in the low DEF inducement protocol. Ifafter the vehicle begins operating in the low DEF inducement protocolthe DEF in the tank freezes, then the three discrete level sensors inthe tank may not properly detect a refill of the DEF, thereby causingthe vehicle to continue operation in the low DEF inducement protocol.

When it is determined that the DEF is at least partially frozen and thevehicle is not currently operating in the low DEF inducement protocol,indicated at 56, then the method 20 may further include defining thetemporary minimum DEF mass to prevent initiation of the low DEFinducement protocol, block 58. When in the frozen DEF protocol, thevehicle bypasses the mass determination based upon the filtered signalsfrom the three secrete level sensors, and instead initializes the DEFmass with the last known value of the DEF mass remaining in the tank.The strategy then calculates the DEF mass remaining by subtracting theDEF that has been dosed from the initialized value of the DEF mass. TheDEF mass remaining in this mode is not allowed to drop below a definedtemporary minimum DEF mass. The value of the temporary minimum DEF massmay be set to any suitable value in order to ensure that the vehicledoes not enter into the low DEF inducement protocol.

When it is determined that the DEF is at least partially frozen and thevehicle is not currently operating in the low DEF inducement protocol,then the method 20 further includes disabling a DEF refill detectionprotocol, block 60. Because the refill detection protocol uses thefiltered signals from the three discrete level sensors in the tank, therefill detection protocol does not function properly when the DEF isfrozen and not sloshing around in the tank.

When it is determined that the vehicle is currently operating in the lowDEF inducement protocol and the DEF is at least partially frozen,indicated at 62, then the method 20 further includes heating the DEF inthe tank to thaw the DEF, block 64, and sensing a partially thawed levelof the DEF in the tank with at least one of the three discrete levelsensors, block 66. As described above, the tank includes the heater forheating the DEF. The heater may include any suitable type, style, sizeand/or configuration of heater suitable for the tank. The method 20further includes defining a partially thawed DEF mass based upon thesensed partially thawed level of the DEF in the tank to permit exit ofthe vehicle from the low DEF inducement protocol, block 68. Because theDEF may not be completely thawed when detected by the discrete levelsensors of the tank, the value for the partially thawed DEF mass isassigned based upon the highest level of the discrete level sensor thatis detected once the DEF begins to thaw. For example, if the DEF isfrozen, and only the second sensor of the three discrete level sensorsdetects the DEF, then the partially thawed DEF mass is assigned a massvalue that is associated with the second sensor of the three discretelevel sensors, whether that is the accurate mass or not. This allows thevehicle to exit from the low DEF inducement protocol when the DEF is atleast partially frozen.

The method 20 may continue to operate in a loop, indicated at 70 and 72.Accordingly, the controller continuously monitors the temperature of theDEF in the tank, and the operation of the vehicle as described above,and changes the operation of the vehicle between the non-frozen DEFprotocol and the frozen DEF protocol as required.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

The invention claimed is:
 1. A method of controlling a vehicle thatutilizes a diesel emission fluid stored in a tank, the methodcomprising: determining if the diesel emission fluid is at leastpartially frozen; determining if a controller of the vehicle iscurrently operating the vehicle in a low diesel emission fluidinducement protocol; and defining a temporary minimum diesel emissionfluid mass with the controller to prevent initiation of the low dieselemission fluid inducement protocol by the controller when the controllerof the vehicle is not currently operating the vehicle in the low dieselemission fluid inducement protocol, and when the diesel emission fluidis at least partially frozen.
 2. A method as set forth in claim 1further comprising defining a frozen diesel emission fluid temperature.3. A method as set forth in claim 2 wherein determining if the dieselemission fluid is at least partially frozen comprises sensing atemperature of the diesel emission fluid in the tank.
 4. A method as setforth in claim 3 wherein determining if the diesel emission fluid is atleast partially frozen further comprises determining if an engine of thevehicle is operating or is not operating.
 5. A method as set forth inclaim 4 wherein determining if the diesel emission fluid is at leastpartially frozen further comprises defining a minimum engine off timewhen the engine is not operating.
 6. A method as set forth in claim 5wherein determining if the diesel emission fluid is at least partiallyfrozen further comprises measuring an engine off time period.
 7. Amethod as set forth in claim 6 wherein determining if the dieselemission fluid is at least partially frozen further comprisesdetermining if the sensed temperature of the diesel emission fluid inthe tank is less than the frozen diesel emission fluid temperature orgreater than the frozen diesel emission fluid temperature, and if themeasured engine off time period is less than the minimum engine off timeor greater than the minimum engine off time.
 8. A method as set forth inclaim 7 wherein determining if the diesel emission fluid is at leastpartially frozen is further defined as determining that the dieselemission fluid is at least partially frozen when the sensed temperatureof the diesel emission fluid in the tank is less than the frozen dieselemission fluid temperature.
 9. A method as set forth in claim 7 whereindetermining if the diesel emission fluid is at least partially frozen isfurther defined as determining that the diesel emission fluid is not atleast partially frozen when the sensed temperature of the dieselemission fluid in the tank is greater than the frozen diesel emissionfluid temperature, and the measured engine off time period is greaterthan the minimum engine off time.
 10. A method as set forth in claim 9further comprising operating the vehicle in a non-frozen diesel emissionfluid protocol when the diesel emission fluid is determined to be not atleast partially frozen.
 11. A method as set forth in claim 4 whereindetermining if the diesel emission fluid is at least partially frozenfurther comprises defining a minimum ambient air temperature limit whenthe vehicle is operating.
 12. A method as set forth in claim 11 whereindetermining if the diesel emission fluid is at least partially frozenfurther comprises sensing an ambient air temperature.
 13. A method asset forth in claim 12 wherein determining if the diesel emission fluidis at least partially frozen further comprises determining if the sensedtemperature of the diesel emission fluid in the tank is less than thefrozen diesel emission fluid temperature or greater than the frozendiesel emission fluid temperature, and if the sensed ambient airtemperature is less than the minimum ambient air temperature limit orgreater than the ambient air temperature limit.
 14. A method as setforth in claim 13 wherein determining if the diesel emission fluid is atleast partially frozen is further defined as determining that the dieselemission fluid is at least partially frozen when the sensed temperatureof the diesel emission fluid in the tank is less than the frozen dieselemission fluid temperature, and the sensed ambient air temperature isless than the minimum ambient air temperature limit.
 15. A method as setforth in claim 13 wherein determining if the diesel emission fluid is atleast partially frozen is further defined as determining that the dieselemission fluid is not at least partially frozen when the sensedtemperature of the diesel emission fluid in the tank is greater than thefrozen diesel emission fluid temperature and maintained for a minimumvehicle operating time, or the sensed ambient air temperature is greaterthan the minimum ambient air temperature limit and maintained for aminimum vehicle operating time.
 16. A method as set forth in claim 15further comprising operating the vehicle in a non-frozen diesel emissionfluid protocol when the diesel emission fluid is determined to be not atleast partially frozen.
 17. A method as set forth in claim 1 furthercomprising disabling a diesel emission fluid refill detection protocolwhen the diesel emission fluid is at least partially frozen, and thevehicle is not currently operating in the low diesel emission fluidinducement protocol.
 18. A method as set forth in claim 1 furthercomprising heating the diesel emission fluid in the tank when the dieselemission fluid is at least partially frozen to thaw the diesel emissionfluid.
 19. A method as set forth in claim 18 further comprising sensinga partially thawed level of the diesel emission fluid in the tank with aplurality of discrete level sensors when the vehicle is currentlyoperating in the low diesel emission fluid inducement protocol.
 20. Amethod as set forth in claim 19 further comprising defining a partiallythawed diesel emission fluid mass based upon the sensed partially thawedlevel of the diesel emission fluid in the tank when the vehicle isoperating in the low diesel emission fluid protocol to permit exit ofthe vehicle from the low diesel emission fluid inducement protocol.